Deep-Sea Vent Discovery Sets Hydrothermal Life’s New Depth Record

A hydrothermal vent found more than 16,000 feet under the sea could harbor life unlike any other yet found, adapted for conditions so extreme that water gas and liquid no longer have separate states.

The vent is one of three discovered on the Mid-Cayman Rise, part of a vast and largely unexplored ridge of spreading ocean crust. Also discovered was the second known example of a type of vent that may resemble seafloor conditions on Jupiter’s moon Europa.

Detected from chemical traces that billow into the ocean like smoke from a smokestack, the vents now await further investigation.

“Every time you get a hydrothermal system, it’s wet and hot, and you get water and rocks interacting. Wherever this happens on the seafloor, life takes advantage,” said geophysicist Chris German of the Woods Hole Oceanographic Institute. “Every time you find seawater interacting with volcanic rock, there’s weird and wonderful life associated with it.”

Because it was impractical to look for vents along the the 60-mile-long Mid-Cayman Rise with seafloor vehicles that can see just a few feet into the murk, German’s team searched in deep-sea water for telltale chemical traces emitted. Once found, they follow the chemicals’ concentration gradient back to their source.

Of the three new vents, described July 19 in the Proceedings of the National Academy of Sciences, one belonged to a category known only from the so-called Lost City hydrothermal field. These are cooler than other deep-sea vents, rich in organic compounds, and suffused by methane. Something similar to those conditions, which at Lost City support life forms unlike any others seen on Earth, may be found under the seas of Europa, one of Jupiter’s four major moons and a prime candidate for non-Earthly life. German’s team named the new vent Europa.

The two other vents have chemical profiles more typical of hydrothermal vents, but one — dubbed Piccard, after deep-sea explorer Jacques Piccard — is 16,000 feet down, a full 2,600 feet below the previous deepest-known vent.

At that depth, high temperatures and pressures could push water to its “critical point,” at which distinct liquid and gas phases cease to exist, and “the physics change completely,” said German. “There’s a whole set of theories about what could happen” to life in those conditions, “but nobody has been able to find this in the real world,” he said. “There’s a whole bunch of questions there.”

Deep-sea bacteria isolated from the water samples hint at this life, but closer inspection awaits the refinement of remote-controlled deep-sea submersibles. At such depths, current submersibles are too difficult to control, said German.

Despite the new vents’ significance, however, they may not be unique. Scientists have explored only a small fraction of the 50,000-mile-long mid-ocean ridge, of which the Mid-Cayman Rise is just one particularly accessible part. Moreover, the planetary crust sliding beneath the Mid-Cayman Rise moves very slowly; for years, these slow-spreading regions, which account for half of the mid-ocean ridge, were thought to have have no hydrothermal activity at all. They’ve barely been explored.

“There could be more of these sites, but nobody has searched systematically,” said German. “The closer we look, the more we’ll find.”

Images: 1) Top left, a carbonate formation at the Lost City site; top right, six-foot-long tubeworms from the Rosebud vent field./WHOI. 2) Map of the three new Mid-Cayman vent locations./WHOI.